1. Field of the Invention
Embodiments of the present invention relate generally to cartridges and modifications for an M16/AR15 rifle.
2. Description of the Related Art
Domestic Law Enforcement Needs
Most domestic law enforcement agencies in the United States utilize the AR15/M16 rifle platform in the course of their daily duties, as patrol officers out on the street; it is often referred to as a “patrol carbine” and is carried by individual officers. These rifles are also used by SWAT teams for room entry or close quarter's battle (CQB) for close in shooting, and are used by some departments as short range sniper rifles. The reasons for the selection of this rifle platform are that they are readily available in many configurations and are fairly reasonably priced to Law Enforcement agencies, the AR15's weight and size are also attractive features of the AR15 as they are easily operable by large men and smaller stature women. The limiting factor is the cartridge that it fires, the 223 Remington, most commonly using a 55 grain bullet. Domestic law enforcement is not held to the military restriction of using full metal jacket projectiles and therefore can choose from a wide variety of available bullet styles and designs, which makes the 223 Remington more effective.
Even with the proper selection of ammunition, the 223 Remington is still substandard for most law enforcement applications and has a well known reputation for “over penetration” with it's small-fast bullet. This can result in extremely dangerous situations for patrol officers working in a built up urban environment. The small weight or mass of the bullet makes it less effective and more prone to deflection on vehicles when engaged by police, especially when engaging thick windshield glass. Although there are a few “alternate” cartridges available that will function in the AR15 rifle, they do not offer enough of an improvement over the existing .223 Remington cartridge chambering to justify the cost in switching over to them, mainly cost and availability of ammunition and magazines. Thus the agencies are limited on their choices of cartridge choices if they maintain the AR15/M16 rifle platform as their weapon of choice.
The other choice for law enforcement agencies is the larger and more costly AR15 “style” rifle made by various companies that fire the .308 Winchester cartridge. The .308 Winchester is a powerful cartridge and offers a substantial improvement over the much smaller .223 Remington chambering. Most police sniper rifles are chambered in the .308 Winchester and are bolt action guns, which do not allow for quick follow up shots if needed.
When quick follow up shots are required the larger AR15 style rifles are sometimes used, they are heavier and have more recoil than the smaller rifles, but deliver ample firepower when needed. These heavier and larger rifles are not the preferred option for SWAT teams for use in room entry and building clearing operations because the power of the 308 Winchester is too much for inside building operations, due to muzzle blast, recoil, and over penetration.
These two calibers represent not only the two most popular calibers used in law enforcement but are the two extremes, with the 223 Remington not providing enough performance or power and the 308 Winchester providing too much or excessive power.
United States Military Needs
The existing standard cartridge or chambering for the military's M16 rifle is the .223 Remington or 5.56 mm NATO (military designation) cartridge. It fires a .224 caliber bullet weighing 62 grains in the military issue M855 ammunition. Bullets weighing as much as 77 grains are currently in use by the US military to increase the performance of the 5.56 mm NATO cartridge and have increased the terminal performance of the cartridge, but its terminal effects are still less than desirable for what is considered an adequate combat cartridge. The shortcomings in the performance of the 5.56 mm NATO cartridge are well documented in current and past military conflicts, and the cartridge's ineffectiveness is more pronounced when the enemy combatants are under the influence of drugs that affect the central nervous system.
An alternative for heavier machine guns is the .308 or 7.62 mm caliber bullet. The most common military caliber utilizing the .308 or 7.62 mm caliber bullet is the 308 Winchester or 7.62 mm NATO cartridge. The performance of the 7.62 NATO is also well documented in combat and is known for its increased stopping power. The U.S. M14 rifle fires the 7.62 mm NATO cartridge as does the U.S. M240 machinegun, as well as several aircraft mounted machineguns and the mini-gun. The AK47 also utilizes a 7.62 mm bullet.
What is needed is a cartridge that will provide improved stopping power without over penetrating, and is compatible with the standard size M16/AR15 rifle platform.